1. Field of the Invention
The present invention relates to a decoder for a pay television system and, more particularly, to a decoder suitable for a pay television system using CATV broadcasting or DBS broadcasting.
2. Description of the Prior Art
Broadcasting systems include CATV (cable television) systems and DBS (direct-broadcasting satellite) systems. These systems frequently are used for pay television systems using an appropriate converter.
In a pay television system of this type, a conventional decoder for decoding a program of a desired channel has mainly two status modes: a free mode and a pay mode. The free mode allows free reception of a TV program, and the pay mode represents a status mode in which a subscriber is charged for reception of a TV program.
More particularly, the pay mode is further classified into a flat fee mode, a tier level pay mode and a pay-per-view mode. In the tier level pay mode, a tier level representing the rank of programs to be received by the decoder is predetermined. A user subscribes to a desired tier level and pays fees to a broadcast station corresponding to the subscribed tier level. In the pay-per-view mode, the user reserves desired programs and pays the program fee only for the reserved programs to a broadcast station.
In the conventional pay-per-view mode, user procedures are cumbersome. When the user wishes to watch a pay program in the pay-per-view mode according to a first conventional procedure, the broadcast station mails a program schedule to each user. The user telephones the center by a predetermined date before a desired program is to be broadcast (i.e., a week or a day beforehand) so as to reserve the desired program. At this time, the user pays the fee for the program. When the desired program is on the air, the center sends a reservation confirmation signal (hereinafter referred to as an ID signal) to a user who has reserved the corresponding program. When a user's receiver or a decoder in the receiver receives the ID signal, a scrambled program signal is descrambled by the decoder, so that the user can watch the desired program.
In the pay-per-view system described above,
(A) the user must telephone the center to reserve the desired program, which is cumbersome and may be inconvenient,
(B) each program has a reservation due date, so that the user cannot reserve the desired program when the reservation due date has passed,
(C) fees cannot be refunded even if the user does not watch the reserved program, and
(D) an idle time is required to send the ID signal to all reserved users at the beginning of every reserved program.
According to a second conventional technique which represents an improvement on the first conventional techique, a pay-per-view status signal is sent from the center to each user. When the user wishes to watch a program represented by the pay-per-view station signal, he depresses a pay-per-view switch located on his tuner. The scrambled program is then descrambled, and the user can watch the program. When the user actually watches the program, charge data transmitted with the subscribed program is stored in an account memory of the decoder. The center periodically checks the contents of the account memory of each decoder, using a telephone line, and collects fees or bills the applicable charge.
The second conventional technique effectively solves the drawbacks of the first conventional technique. However, since the center must periodically check the account memories of all users, the check system is complicated. Furthermore, since fee collection is performed by use of a telephone line, an auto-dial unit and a modem (modulator/demodulator) are required, so that the required user unit and center unit are complex and expensive.